Polyoxymethylene (polyacetal) is an extraordinary material from which the most varied articles may be produced, in particular by injection molding. An advantageous feature is, in particular, its chemical resistance against many organic solvents and also bases. Since the introduction of polyacetals onto the market, attempts have been made to reduce the acid lability arising from their chemical structure. Unless protective measures are taken, the repeating acetal structure in the polymer chain has unstable semi-acetal terminal groups from which polymer degradation proceeds. In order to stabilize the polymer, its terminal groups may be protected by esterification or etherification, as described in H. Cherdron, L. Hohr, W. Kern, Makromol. Chem., 52, 48 et seq. (1962). Another method is to incorporate comonomers which form a stable terminal group on degradation of the polymer chain. This makes polyoxymethylene (POM) fit for everyday use, but the acid lability remains, since (c.f. V. V. Pchelintsev, A. Yu. Sokolov, G. E. Zaikov, Polym. Degradation and Stability, 21(4), 285 (1988)) acid catalyzed hydrolytic decomposition of POM may take place at any location on the polymer such that stabilized terminal groups or comonomer units do not provide sufficient protection. It is known from German patent DE 11 93 240 that high proportions of a urethane scavenge the formaldehyde arising from acidolysis An example of this is a molded article with 40% POM. In this way, the odor problems or hazard to health caused by liberated formaldehyde are reduced, but the POM is still degraded. Moreover, a product with 40% POM / 60% TPU no longer has a POM matrix so that the advantageous properties of ROM (e.g. stiffness) are lost. German patent DE 12 35 585 describes the acylation of POM with carbodiimide. This considerably reduces acidolytic degradation of the polymers by free acetic acid. The carbodiimide is, in particular, intended to provide stabilization for the transient acid conditions during esterification. Investigations have, however, shown that the products produced in this manner are also unsuitable for use under acidic conditions.
It is furthermore known, for example from German patent DE 25 40 207, to add basic substances, such as salts for example, to the POM to provide protection from the acidic conditions arising during production and processing. The basic substances act to neutralize acidic components in the polymer and so only those salts whose acidic portion does not itself attack the POM are suitable. Thus, for example, a small quantity of sodium carbonate may be added to a polyoxymethylene. The products so obtained are also unsuitable for use under acidic conditions.